Fiber optics have been in use for many years, in applications such as medical endoscopes, cathode ray tube faceplates, flexible light distribution bundles, automobile indicator lamps, and borescopes, which require light transmission of a few meters at most. More recently, fiber optics have entered the telecommunication field, transmitting signals over distances several orders of magnitude longer. For a survey of the development of fiber optics, see 10 Kirk-Othmer Encyclopedia of Chemical Technology 125 et seq. (3rd ed., 1980).
U.S. Pat. Nos. 4,441,787 to Lichtenberger and 4,653,851 to Pedersen et al. teach fiber optic cables and methods for manufacturing the same. The Lichtenberger and Pedersen et al. patents are incorporated herein by reference for the details of fiber optic cable design and manufacture. U.S. Pat. No. 4,749,059 to Jonnes et al. teaches a cable lubricating device useful for applying grease to a fiber optic cable, and is incorporated herein by reference.
U.S. Pat. No. 4,602,763 to Gaylin discloses a method for drawing a fiber optic cable through a conduit, and is incorporated herein by reference.
U.S. Pat. No. 4,688,890 to DeMeo et al. relates to a fiber optic cable innerduct for containing and protecting fiber optic cable and for reducing the drag on fiber optic cable as it is pulled through the innerduct. The DeMeo et al. patent is incorporated herein by reference.
The fiber optic cables used commercially typically comprise an inner optic fiber surrounded by a protective sheath. The optic fiber is typically lubricated, and the outer shell of the protective sheath may also be lubricated to reduce friction when drawing the assembly through a conduit for installation. Proper lubrication between the optic fiber and the protective sheath helps to minimize microbending and the concomitant signal loss. Further, the cushioning effect of a viscous lubricant renders the optic cable assembly more resistant to impact damage. See the Lichtenberger'787 patent at column 2, lines 26-69, and also column 5.
The telecommunications industry needs optic cable assemblies which can be easily installed (e.g., buried underground) and then operated for decades without maintenance. Thus the cable filler material or lubricant must not only be thermally and oxidatively stable, but must also be inert to the cable sheath material. Additionally, the cable filler material should be resistant to biodegradation. The optic cables should also be suitable for installation and use over a wide range of temperatures, particularly in cold winter conditions. The goals of lubricant inertness (including thermal and oxidative stability, as well as resistance to biodegradation) and substantially constant viscosity and lubricity over a broad range of temperatures have, in the past, been in conflict because lower molecular weight solvents (which tended to deteriorate the cable sheath material) were required to attain the desired low temperature viscosity and lubricity characterisitics.
Efforts to improve upon the performance of natural mineral oil based lubricants by the synthesis of oligomeric hydrocarbon fluids have been the subject of important research and development in the petroleum industry for at least fifty years and have led to the relatively recent market introduction of a number of superior polyalpha-olefin synthetic lubricants, primarily based on the oligomerization of alpha-olefins or 1-alkenes. In terms of lubricant property improvement, the thrust of the industrial research effort on synthetic lubricants has been toward fluids exhibiting useful viscosities over a wide range of temperature, i.e., improved Viscosity Index, while also showing lubricity, thermal and oxidative stability and pour point equal to or better than mineral oil. To match synthetic lubricants with their intended application, these lubricants have, in the past, been formulated for specific properties. For example, poly-alpha-olefins (PAO) were produced from 1-decene polymerization over promoted BF.sub.3 or AlCl.sub.3 catalysts. While poly-alpha-olefins are useful components in fiber optic cable filler materials, it would be desirable to provide fiber optic cable filler materials with still further improved lubricity, oxidative stability, thermal stability, and resistance to biodegradation over a broad range of temperatures.